1. Field of the Invention
The present invention relates to a coil device such as a transformer and an inductor to be used for electronic equipment, switching power supply apparatus or the like, and the switching power supply apparatus using it.
2. Description of the Related Art
Switching power supply apparatus have been widely used for a power supply units of various electronic devices such as personal computers, facsimile machines or the like. Especially, switching power supply apparatus including an isolated forward converter type as a DC-DC converter are suitably employed in laptop computers or the like.
Such a switching power supply apparatus including an isolated forward converter generally comprises a power transformer, a driving transformer and a choke coil. These coil elements use coils and core parts, which are bulky and require substantial spaces to be mounted on a circuit board. As a result, it is very difficult to miniaturize the circuit board and switching power supply apparatus itself.
In addition, transformers and choke coils are relatively expensive elements due to the fact that manufacturing methods of these elements include a step which cannot be automatically processed. It is difficult to reduce the cost of the switching power supply apparatus, accordingly.